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Population Growth and
Regulation
Characteristics of Populations
Demographics are characteristics of
populations
Populations can be characterized by their:
Population Size
Population Density
Population Distribution
Age structure
Reproductive base
# Reproductive and younger
Age Structure Diagram
Green - Pre-reproductive years
Dark Blue- Reproductive years
Light blue - Post- reproductive years
Age Structure Diagram U.S.
Zero growth:
#births = #deaths and #immigrate = #emigrate
Regarding Population Density:
The same area may be home to many
species but they may vary by density
Density refers to the number of
individuals in an area but not how they
are dispersed
Population density variations are largely
due to ecological relationships and
organism interactions in an area
Population Size and
Exponential Growth:
How population size changes
Size depends on births,
immigration, deaths, emigration
and migrations
Zero population growth is a near
balance between all the positive and
negative factors
Ground Zero to Exponential
Growth
Increase in population
of field mice
J Shaped Growth Curve
Effects of Deaths on
Populations
The effects of deaths on the
rate of increases in 2
bacterial populations
Regarding the Biotic Potential:
The biotic potential of a population is
its maximum rate of increase under ideal
conditions
Biotic potentials vary from species to
species based on:
What age reproduction begins
How frequent reproduction is
How many offspring are born at a time
Limits on the Growth of Populations:
The actual rate of growth depends on the
environmental conditions
Limiting factors are collectively called
environmental resistance and include:
Nutrient supply
Predation
Competition for space
Pollution
Metabolic wastes
Limiting Factors on Growth
The sustainable
supply of
resources defines
the carrying
capacity for a
population in an
environment
The capacity can
vary over time
Note the S
shaped logistic
growth
Carrying Capacity
Density - Dependent Controls:
 The main controls are:
Competition for resources
Predation
Parasitism
Disease
 They exert their effects in proportion to the
number of individuals present
 Density - dependent factors
Events resulting in more deaths
Fewer births
Paramecium caudatum
Paramecium aurelia
Fig. 48.4, p. 856
PREY
POPULATION
PREDATOR
POPULATION
Fig. 48.7, p. 858
Fig. 48.8, p. 859
Density Independent Factors:
Some events such as weather tend to
increase the death rate without respect to
the number of individuals present
Lightning, floods, snowstorms affect both
large and small populations!
Life History Patterns:
Life Tables
Demography
is the study of
the age-specific
patterns of
particular
populations
Life tables
follow the fate
of a group
(cohort) and
calculate
survivorship
schedules
A note on…
Human Population Growth
Increase in growth rate
Expansion of habitat
Increased capacity in existing habitats
Population has sidestepped limiting factors
Technology
Medicine
Population Growth Rate in
Different Regions
Population Growth Rate in
Different Regions
1996 - Orange
2025 - Blue